While traditional ground-glass telescope mirrors offer very-high-quality imaging, they are very expensive and difficult to make. This invention promises to reduce the price of a one-meter primary mirror, currently costing on the order of $100,000, to under $1,000. It can also reduce or eliminate optical aberrations due to creep, flex, or thermal expansion and contraction.
U.S. Pat. No. 6,679,611, which issued on 20 Jan. 2004 to Robert J. Howard and is titled “Adaptive, Aluminized Mylar Mirror,” is incorporated herein by reference. Howard describes an infrared beam directed to the surface of a Mylar mirror, and the mirror reflects that beam. The reflected beam is detected, and data gleaned from the reflected beam is used to determine whether the optics of the mirror must be adjusted. The optics of the mirror are adjusted by varying voltage applied to electrostatic actuators on the frame of the mirror, or varying the pressure in chambers formed by the mirror frame and mirror surface.
U.S. Pat. No. 6,754,006 entitled “Hybrid metallic-dielectric grating” issued Jun. 22, 2004 to Barton et al. and is incorporated herein by reference. This patent describes a diffraction grating having a metallic base layer and layers of dielectric materials of varying refractive index, where a bottom interface of the layers is adherent to the metallic base layer. The dielectric layers are periodically spaced on top of the metallic base layer, leaving the metallic base layer exposed in regions. This grating allows for the polarization-insensitive reflective properties of the base metallic layer to operate in conjunction with the polarization sensitive diffraction properties of the multilayer grating structure to provide near 100% diffraction efficiency over a reasonable wavelength bandwidth, independent of the polarization of the incident beam.
U.S. Pat. No. 5,907,436 entitled “Multilayer dielectric diffraction gratings” issued May 25, 1999 to Perry et al., and is incorporated herein by reference. This patent describes the design and fabrication of dielectric grating structures with high diffraction efficiency. The gratings have a multilayer structure of alternating index dielectric materials, with a grating structure on top of the multilayer, and obtain a diffraction grating of adjustable efficiency, and variable optical bandwidth.
Other background to the present invention is described in a book chapter titled “Experiments with Pneumatically-Formed Metalized Polyester Mirrors,” by Bruce D. Holenstein, Richard J. Mitchell, Dylan R. Holenstein, Kevin A. Iott and Robert H. Koch, that appears in Genet, Johnson, & Wallen, Eds. (2010), “The Alt-Az Initiative: Telescope, Mirror, & Instrument Developments.”
The concept of a flexible mirror is not new. A 1988 technical-report publication by Waddell, titled “Development of a stretchable concave imaging membrane mirror of variable focus,” describes a membrane mirror which is shaped by differences in air pressure. European Patent Application Publication EP 0252034 A2 of Ugo, published 7 Jan. 1988 and titled “Electronic corrector of curvature defects on image, for telescopes provided with large diameter light weight catoptric parts, to be used in orbit as well,” is incorporated by reference. Ugo describes projecting a laser onto a telescope-mirror surface to obtain actual curvature characteristics of a telescope mirror, comparing the actual telescope-mirror surface characteristics against an ideal model, and calculating discrepancies between the two, and subsequently using the data for correcting telescope images.
What is needed, and what the present invention provides, is a refined control system for a flexible mirror to achieve greater optical acuity.